The present invention relates generally to coupling means for a snow plow and, more specifically to automatic coupling and uncoupling means.
A conventional snow plow includes framework which is fixed to the back of the plow. The framework is adapted to be connected to an "A-frame" which is provided with hydraulic actuating means for angling the plow. The "A-frame" is also provided with coupling means for coupling with complimentary coupling means of framework which is attached to the front of the plow vehicle. This latter framework is generally referred to as a "push beam" and includes a pair of spaced guides for receiving a pair of spaced tabs which extend rearwardly from the "A-frame". Each tab has a plurality of apertures and is adapted to fit into one of the guides of the "push beam". A retractable connecting pin is associated with each guide. The pin extends laterally through apertures in the guide and through one of the apertures of the tab, when the tab is positioned within the guide, so that one of the apertures of the tab is axially aligned with the apertures of the guide.
During periods when the plow is not being used, it is disconnected from the vehicle and stored in a location where the vehicle can be driven up to the "A-frame" of the plow for recoupling. Normally, the "A-frame" is mounted on blocks at a height which enables the tabs to be at the same height as the guides in the "push beam". The connecting pins are pulled out of the guides and the vehicle is advanced toward the "A-frame", so that the tabs enter the guides. Most of the time, the apertures in the guides are misaligned within the guides by means of lift chains which are connected to a hydraulically operated lever in the vehicle. After the apertures in the guides are aligned with corresponding apertures in the tabs, the connecting pins are reinserted into the guides and through the tabs. The entire operation of coupling the plow to the plow vehicle is awkward and time-consuming, particularly if the entire operation is performed by a single individual. First of all, it is extremely difficult for an individual to advance the vehicle toward the "A-frame", so that the tabs are horizontally aligned with the guides. Very often, several attempts must be made before the tabs are generally aligned with the guides, so that they can be advanced into the guides. The individual must make several trips into and out of the vehicle. When the operation is performed by two individuals, one individual can stay in the vehicle while the other individual attempts to direct the movement progress of the vehicle. Even with two individuals, several reciprocations of the vehicle must be made before the tabs are aligned within the guides. Thereafter, the "A-frame" must be manipulated vertically to properly align the apertures of the guide with corresponding apertures in the tabs. Under ideal weather conditions, the entire coupling operation is difficult enough. However, most of the time weather conditions are substantially less than ideal. In most cases, snow plowing begins in the early morning hours when it is dark. There is always a certain degree of emergency to get started and coupling under less than ideal conditions can be very frustrating to the operator.
After plowing has been completed, the task of uncoupling the plow from the vehicle is just as difficult as the task of coupling the plow to the vehicle. After the plow has been lowered to the mounting blocks, the connecting pins are removed from the tabs. If the plow frame is not at the precise vertical position, there is downward or upward pressure on the pins which causes them to bind and makes it difficult, if not impossible, to pull out.
An automatic coupling for snow plows has been developed and shown in U.S. Pat. No. 4,619,060 to Leland P. Knowlton, one of the inventors of the present application. Under ordinary operating conditions, the device which is shown in the Knowlton functions exactly as intended. The coupling mechanism which is disclosed in this patent enables the plow to be coupled and uncoupled automatically. However, under certain unusual or extreme conditions, it is possible for unwanted uncoupling to occur. An example of such unusual circumstances are plowing on an uneven surface as for example, having one wheel on the sidewalk and the other wheel on the road. Another example of an unusual circumstance is misalignment of the coupling plates due to damage to the supporting frame for the plow.
The principle object of the present invention is to provide a plow coupling which enables a plow to be coupled and uncoupled automatically and which prevents uncoupling in unusual or extreme circumstances.
Another object of this invention is the provision of a plow coupling which enables a plow to be coupled and uncoupled automatically and which includes safety retaining means which positively prevent accidental uncoupling of the plow during a plowing operation.
A further object of the present invention is the provision of an automatic coupling and uncoupling mechanism for a snow plow with a hand actuated retaining mechanism which prevents accidental uncoupling of the plow during plowing and which is simple in construction and easy to operate.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.